1. Field of the Invention
This invention relates to the field of integrated circuits and, more particularly, to test circuits and memory devices.
2. Description of the Related Art
Circuits such as static ram (SRAM) cells are widely used as computer memory to store bits of information. SRAM is used particularly in applications where access speed is required because SRAM cells provide relatively fast access times compared to their dynamic RAM counterparts. However, SRAM devices may be more expensive to manufacture. Thus, SRAM arrays are typically used in processor cache memory, while DRAM devices are typically used as computer system main memory due to such factors as cost. One issue with manufacturing the SRAM cells is depending on process parameters during manufacturing, it may be possible for the read current associated with each SRAM cell to vary from cell to cell and between manufacturing lots. This variability may present reliability problems, particularly when attempting to design associated sense amplifiers for the SRAM cells.
The manufacturing of integrated circuits is a complex process. Bringing a new circuit design to a fabrication facility, or bringing an existing circuit design to a new fabrication facility may require a number of characterization steps to establish a device library. Depending on the process technology, and the complexity of the circuits, there may be several iterations of process adjustments to ensure reliable operation of the manufactured devices. In many cases, there may be several revisions of silicon before the design is fully operational. Accordingly, it may be desirable to provide a robust circuit design while reducing the number of iterations of process adjustments, particularly during device and process characterization.